Electronically controlled fuel injection systems are becoming more widespread for use with diesel engines. One example of such a system is the amplifier piston common rail system (APCRS) illustrated in the paper “Heavy Duty Diesel Engines—The Potential of Injection Rate Shaping for Optimizing Emissions and Fuel Consumption”, presented by Messrs. Bernd Mahr, Manfred Durnholz, Wilhelm Polach, and Hermann Grieshaber; Robert Bosch GmbH, Stuttgart, Germany, at the 21st International Engine Symposium, May 4-5, 2000, Vienna, Austria. In the Bosch fuel injection system, a controlled leakage strategy is utilized to control opening and closing of the needle. For instance, for pre-injection and the first portion of a main injection having a boot rate trace, fuel is directed along a by-pass route. After the main injection has begun, a pressure intensifier piston is activated for the required pressure controlled injection. While this system shows promise, there is still room for improvement.
Recently, engineers have determined that the performance of fuel injectors, including those used in common rail fuel injection systems, can be increased, and undesirable emissions reduced, by controlling the mass flow rate of fuel injected into a combustion chamber during an injection event. It is also believed that the ability to front end rate shape an injection event can further reduce emissions while increasing fuel injector performance. While a number of fuel injectors have been developed that have limited rate shaping capabilities, the ability to produce some front end rate shapes has not been possible. Therefore, a fuel injector having a broader range of front end rate shaping capabilities would allow greater flexibility for further reduction of undesirable emissions while allowing for improved fuel injector performance.
The present invention is directed to overcoming one or more of the problems as set forth above.